A vehicle power supply system that stores battery modules is installed in an electric vehicle or a hybrid electric vehicle that uses a motor as a drive source (e.g., refer to Patent Literatures 1, 2). This type of vehicle power supply system includes a battery cooling unit for holding the temperature of a battery within a proper temperature range to prevent the deterioration in performance of the battery that is caused when the temperature of the battery is increased abnormally, and it is required to cool the battery modules as uniformly as possible in this battery cooling unit. For example, in a vehicle power supply system described in Patent Literature 1, air discharged from a cooling fan is divided to be supplied to two battery modules, whereby variation in cooling effect is suppressed.